An erasable and programmable read-only memory (EPROM) is erased by exposing it to ultraviolet (UV) light. To allow for such erasure, the EPROM must utilize a passivation layer which is sufficiently transparent to allow passage of the UV light. A number of EPROMs use oxynitride films for their passivation layer. These films are often deposited using a chemical vapor deposition (CVD) process wherein solid films are formed on an integrated circuit wafer by the chemical reaction of vapor phase chemicals (reactants) that contain the required constituent gases. Three major CVD processes exist: atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), and plasma-enhanced CVD (PECVD). APCVD and LPCVD systems are characterized by the requisite pressure for the deposition. Typically, these system use thermal energy to promote chemical reactions responsible for the film deposition. PECVD systems, however, are categorized by pressure and by its method of energy input. PECVD systems do not rely solely on thermal energy, but instead use a radio-frequency (RF) induced glow discharge plasma to transfer energy into the reactant gases, allowing the integrated circuit wafer to remain at a lower temperature than in APCVD or LPCVD processes.
Typically, in PECVD systems, the films are deposited in low frequency, lower power density batch reactors. Batch reactors accommodate a large number of wafers at the same time. In low power density processes, the RF power is distributed over large numbers of wafers, wherein each wafer is subjected to a low power density plasma. Under these conditions, the deposition time is long. Low frequency processes also have drawbacks. In low frequency processes, the films tend to be very sensitive to device pattern. In other words, a different process is required to fabricate each different type of devices, where each wafer contains different devices. Secondly, low frequency processes tend to produce films which are non-uniform across the wafer. The question of uniformity also arises where the wafer has a variety of devices on it with a varying structure density. Batch systems also have a higher wafer-to-wafer thickness nonuniformity as compared to single-wafer systems.
The present invention avoids these drawbacks by using a high frequency, high RF power density single wafer PECVD process to fabricate a passivation layer of oxynitride on EPROMs. The present invention operates on single wafers, irrespective of device type, to produce a uniform passivation film. Moreover, the present invention has the advantage of being a low particulate process.